A phase contrast microscope has been introduced as a microscope which can observe clear and colorless living cells without killing them by dyeing or the like. This phase contrast microscope can observe clear and colorless specimens with contrast of light and shade, thereby achieving observation of living cells or the like with living condition.    [Patent document 1] Tokukai-hei 9-230247
As mentioned above, the phase contrast microscope can observe clear and colorless living cells with contrast of light and shade. The phase contrast microscope needs to use a phase plate in order to observe items with contrast of light and shade.
The phase plate is formed of a certain thin membrane, and it can advance or delay a phase by one quarter of the wavelength of the light beam by transmitting the light beam outputted by a light source through the thin membrane. Since a material which composes the thin membrane of the phase plate has dispersion, it cannot make a phase lag of one quarter of the wavelength relating to any wavelengths, thereby reducing a contrast when observing specimens using a light beam with wide range of wavelengths. The ordinary phase contrast microscope has a configuration with a colored filter corresponding to the predetermined wavelength in order to observe items using only a light beam with the predetermined wavelength. According to such configuration, the ordinary phase contrast microscope can make a phase lag of one quarter of the wavelength of the light beam.
However, since the ordinary phase contrast microscope has a configuration with a filter, an image of specimens is expressed only by thickness of plain color. A user, therefore, has to observe specimens without having information relating to color of the specimens.